The present invention relates to a surgical technique and instrumentation for the placement, trial, and fixation of an artificial patellar component in primary total knee replacement or revision total knee replacement surgery. Specifically, the present invention relates to a patellar trial consisting of an articular surface member and a fixation peg drill guide for use during knee replacement surgery. The invention can easily be adapted to any patellar component and any fixation method.
The patellar trial and drill guide of the present invention can be used during all surgical techniques for trialing a patellar component prior to establishing fixation peg holes, fixation crosses, or fixation rings during knee replacement surgery. These techniques may include modifying a patellar trial so it can be temporarily fixed to a resected patella, performing a trial reduction with the patellar trial in place, marking the placement of a patellar trial on the patella to aid in using a drill guide for establishing fixation peg holes, and using a patellar trial as a x-ray marker or guide to aid in the placement of artificial replacement implants.
The patella, commonly called the kneecap is the part of the human skeleton that articulates with the femur. The articular surface of the patella is held in place against the distal femur the femoral condyles by the patella tendon. The patella provides the leverage necessary for proper functioning of the knee joint. If the articular surface of the patella decays, or is degenerated, proper functioning of the knee joint is not possible with the constant pain and immobility typically associated with these conditions.
Joint replacement is becoming increasingly widespread. One of the most widely practiced joint replacements involves the knee joint. In many cases, the replacement of the knee joint with prosthesis also involves the replacement of a portion of the patella with a prosthetic implant.
The leading cause of clinical failure of primary total knee replacement, or revision total knee replacement surgeries is patella problems, such as pain and dysfunction of the patella femoral joint. Many patella failures are related to patella misalignment and tracking with the femoral and tibial replacement components and with the knee extensor mechanism. When the patella fails, it frequently cannot be satisfactorily resurfaced, leading to either removal of its components or a patellectomy. These procedures often result in a major compromise to the functioning knee.
Another factor in determining ultimate patella tracking and prosthesis longevity is accurate placement of the patellar prosthesis in the knee. The patella's articulation with the femoral groove and femoral component is especially integral to the longevity and success of the prosthesis.
One method popularized as a way to increase patellar prosthesis longevity is lateral retinacular release. Lateral retinacular release is used to improve patella tracking when the prosthesis does not track properly after is has been surgically implanted. However, several problems associated with lateral retinacular release are well known including increased post-operative hemarthrosis and hematoma. Extensive lateral retinacular release also increases the probability of a vascular necrosis due to the sacrifice of the patellar branch of the superior lateral geniculate artery.
Presently there is no method for trialing a patellar implant before permanent location of the patellar implant is determined and committed to. Also there are no techniques or instrumentation for trialing patellar implants of different thicknesses or diameters. Trialing patella's of different thicknesses or diameters is especially crucial in total knee revision surgery.
The tools available to the surgeon also influence the success of surgical techniques in total knee replacement surgery, and patella longevity. Presently, suitable instrumentation systems and cutting guides for the tibial and femoral components are known in the art. These systems and tools have improved surgeon's abilities to implant the components properly and have reduced failures due to improper tibial and femoral component alignment.
However, there are no known prior art teachings of methods or tools that take into consideration the position of the patella in relation to the trial femur and tibial component before committing to the location of the patellar component.
Existing instrumentation for patellar implant trial and fixation include a series of patellar trials ranging is diameters from approximately 26 mm to approximately 48 mm in 2 to 3 mm increments, a series of fixation peg drill guides of the same diameters, a stop drill or mill, and a patellar clamp. The patellar trials are the exact same shape, diameter and thickness as the patellar implants. Some surgical systems have additional instrumentation for resection or removal of unwanted patellar bone.
Present instrumentation and techniques involve guessing on where the patella should be located on the resected patella, holding a drill or mill guide on the patella, preparing the fixation peg holes in the patella, placing the patellar trial on the patella, and performing a trial reduction. It is during the trial reduction that placement and size of the patella is assessed by the surgeon. This assessment should occur before the patellar fixation peg holes have been established, not after.
While performing the trial reduction and assessing the tracking and placement of the patellar trial, if it is determined that a different sized patella is needed, or that moving the patella to a different location is required, the surgeon is very reluctant to make these corrections. Retrialing a patellar implant is rarely done. Moving the location of the patella or trialing a different sized patella requires committing to a new location for the patella, re-drilling the fixation holes in a different location, placing the new trial in the new fixation holes, and then performing another trial reduction.
The reason these corrections are so rarely made is because re-drilling new fixation peg holes in the patella decreases the strength and integrity of the patella, which can lead to patella fracture, necrosis, pain, and ultimately failure of the implant. The results of this reluctance to correct the placement and/or size of the patellar implant are misalignment or improper sizing of the patellar implant. Misalignment or improper sizing of the patellar implant can cause unwanted retinacular releases, patella dislocations, increased polyethylene wear, pain, and ultimately patellar component failure.
Therefore, there remains a need for a method and apparatus of accurately sizing, aligning, trialing, and implantation of patellar components during knee replacement surgeries. Such a technique and instrumentation would decrease total knee replacement failures, specifically due to patella femoral joint misalignments, polyethylene wear, chronic patella dislocation, necrosis, and fracture. The method and apparatus of the present invention satisfies these needs.